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lsim warning for TF systems #624
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You can ignore that warning if you don't intend to make use of x. x is the "internal state" of the system, and depends on the specific realization of your state-space representation of the transfer function you provided.
Hi @ sawyerbfuller and thanks for the prompt answer. Is there a way to not show the warning? Otherwise I'll just ignore it.
Thanks again,
Marco
Hi Marco,
one way is to use the more pythonic forced_response, which gives you more control, and in particular, I believe you can ask it to not give you x.
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on May 27, 2021
Dear all,
I have just installed control 0.9.0 and when using lsim (or forced_response) on a transfer function system I got the following warning: "return_x specified for a transfer function system. Internal conversion to state space used; results may meaningless."
Can I skip this warning? Is there another function for simulating transfer function systems that does not require a conversion to state space?
I cannot figure out if the warning is something I should worry about or not.
Thanks,
Marco from SIPPY teams
The example tested is the following:
from future import division
from past.utils import old_div
from sippy import functionset as fset
from sippy import *
import numpy as np
import control.matlab as cnt
sampling_time = 1. # [s]
end_time = 400 # [s]
npts = int(old_div(end_time, sampling_time)) + 1
Time = np.linspace(0, end_time, npts)
switch_probability = 0.08 # [0..1]
[Usim,,] = fset.GBN_seq(npts, switch_probability, Range = [-1, 1])
white_noise_variance = [0.01]
e_t = fset.white_noise_var(Usim.size, white_noise_variance)[0]
DEN = [1., -2.21, 1.7494, -0.584256, 0.0684029, 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.]
NUM = [1.5, -2.07, 1.3146]
g_sample = cnt.tf(NUM, DEN, sampling_time)
Y1, Time, Xsim = cnt.lsim(g_sample, Usim, Time)